外源精胺对菜用大豆贮藏冷害及蔗糖代谢的影响

【目的】探讨精胺（Spermine，Spm）处理延缓菜用大豆贮藏冷害以及调节其蔗糖代谢的作用机理，为菜用大豆的采后贮藏保鲜技术提供参考。【方法】以‘新大粒1号’菜用大豆为试验材料，分别用0.5、1 和2 mmol·L^-1外源Spm浸泡处理20 min，以清水浸泡为对照，于1℃、相对湿度为85%-90%的环境条件下贮藏10周，每周分别测定与菜用大豆抗冷性相关的生理指标，籽粒中蔗糖、果糖和葡萄糖含量，及与蔗糖代谢相关的酶活性指标。【结果】贮藏第2周即出现冷害，随着冷藏时间延长，菜用大豆冷害发生逐渐加重。与对照相比，Spm处理使冷害症状出现时间推迟到第3周，延缓了贮藏后期冷害指数的上升；也抑制了菜用大豆细胞膜透性的增加，贮藏5周后，0.5和1 mmol·L^-1 Spm处理与对照的差异均达到显著水平（P＜0.05）；此外，冷藏期间的菜用大豆籽粒中膜脂过氧化产物-丙二醛（MDA）不断积累，低浓度Spm能缓解膜脂过氧化，减少MDA积累，而高浓度Spm可能产生毒害作用；与对照相比，1 mmol·L^-1 Spm明显提高了菜用大豆冷藏期间抗氧化酶-过氧化氢酶（CAT）、过氧化物酶（POD）和超氧化物歧化酶（SOD）的活性；与此同时，Spm处理也显著减少了菜用大豆籽粒蔗糖的损失（P＜0.05），经过Spm处理的菜用大豆籽粒中果糖与葡萄糖含量低于对照，但整个贮藏期不同浓度处理间差异不显著（P＞0.05）。进一步通过冷藏菜用大豆籽粒可溶性糖含量与酸性转化酶（AI）、中性转化酶（NI）、蔗糖合成酶（SS）和蔗糖磷酸合成酶（SPS）4种蔗糖代谢相关酶活性之间的相关性分析发现，蔗糖含量与AI活性呈极显著负相关（P＜0.01），与SPS活性呈极显著正相关（P＜0.01），而与NI和SS活性之间没有显著相关性，说明AI和SPS对菜用大豆冷藏期间蔗糖的降解起到了关键的调节作用，外源Spm通过对蔗糖代谢相关酶活性的调节有效抑制了冷藏菜用大豆籽粒中蔗糖含量的损失。【结论】Spm可有效延缓菜用大豆1℃贮藏期间冷害的发生，最适浓度为1 mmol·L^-1；蔗糖损失可能是导致菜用大豆冷害加剧的重要原因，Spm通过抑制AI活性增加的同时，延缓SPS活性的降低，以维持冷藏期间菜用大豆籽粒较高的蔗糖含量。

Effect of Exogenous Spermine on Chilling Injury and Sucrose Metabolism of Post-Harvest Vegetable Soybean

【Objective】 Mechanism of exogenous spermine in delaying chilling injury and regulating sucrose metabolism of vegetable soybean during cold storage was investigated to provide a theoretical basis for the preservation of post-harvest vegetable soybean. 【Method】 ‘Xindali No. 1’ vegetable soybeans used as the experimental materials were immersed in 0.5, 1 and 2 mmol·L^-1 spermine for 20 min, respectively, distilled water as a control, then stored at 1℃ for 10 weeks under the environmental condition of relative humidity of 85%-90%. The chilling resistance related physiological indexes, soluble sugars (sucrose, fructose and glucose) contents and the activities of sucrose metabolism related enzymes were all determined every week.【Result】 The chilling injury (CI) symptoms of vegetable soybean aggravated with the extension of storage period, and it appeared during the first two weeks of storage. Spermine treatment not only delayed the increase of CI index and postponed the symptoms until the 3rd week, but also inhibited cell membrane permeability, especially after 5 weeks of storage, both 0.5 and 1 mmol·L^-1 spermine treatment groups reached significant levels (P<0.05) compared with the control group. In addition, during cold storage, the membrane lipid peroxidation product, including malondialdehyde (MDA) gradually accumulated in vegetable soybean, low concentration of spermine could reduce the lipid peroxidation and decrease MDA accumulation, while high concentration of spermine had a toxic effect. Compared with the control group, 1 mmol·L^-1 spermine significantly improved the activities of antioxidant enzymes (CAT, POD and SOD) of vegetable soybeans during storage. And meanwhile, spermine treatment also significantly (P<0.05) reduced the sucrose loss of vegetable soybean, fructose and glucose contents in spermine-treated vegetable soybean grains were lower than the control group, but the concentration differences among all treatment groups were not significant (P>0.05) during the whole storage period. Through the correlation analysis between soluble sugars contents and sucrose metabolism related enzyme activities in vegetable soybean grains during cold storage, it indicated that sucrose content had a significant negative correlation (P<0.01) with AI activity, but a significant positive correlation (P<0.01) with SPS activity, and no significant correlation with NI and SS activities, which meant AI and SPS played a key role in sucrose degradation of vegetable soybean during cold storage, exogenous spermine effectively inhibited the sucrose loss by regulating the activities of sucrose-metabolizing enzymes in vegetable soybean.【Conclusion】 Spermine effectively delayed the chilling injury of vegetable soybean during storage at 1℃, and a dose of 1 mmol·L^-1 could be an effective treatment. Sucrose loss might cause the aggravated chilling injury, while spermine maintained higher sucrose content by simultaneously inhibiting the increase of AI activity and the decrease of SPS activity in vegetable soybean during cold storage.